This invention relates generally to illuminating controls or output devices of user interfaces, and more particularly, to using internal reflection to guide light from a source to a surface.
Electronic devices have, in recent years pervaded our society. Driven by new technologies such as calculators, GPS, cellular, remote key-less entry, the industry has spawned a myriad of core device-types. The nature of competition has caused some of these devices to take on additional functionality, and occasionally a convergence of multiple functionalities. The result is, in order to power a multifunction device, conservation of power must be done in a clever way. Unfortunately, the use of LEDs, or illuminated user interfaces in general (e.g. push buttons, back and frontlit LCDs) causes a significant drain on the power source available to such multifunction devices.
Manufacture of electronics devices, particularly those having a quantity of buttons, has been a constant struggle to reduce part-counts. While the older plastic keypads have largely given way to monolithic rubber membranes, a new collection of parts has evolved to supply night time illumination of and through such buttons, namely individual LEDs to match each button. The additional parts increase the costs of manufacture and diminishes the reliability of such illuminated devices.
One of the big costs in terms of using e.g. a lambertian emitting LED to illuminate any part of a user interface, is the fact that only a small fraction of the power provided electrically to the LED actually transfers to optical power. Moreover, guiding this optical power efficiently to the area which is to be illuminated is very difficult. Instead, the LED illuminates through a range of angles that cast light on a large swatch of the interior of the devicexe2x80x94light that is generally wasted. This effect is more pronounced as the LED source is placed farther from the button or LCD that the LED is supposed to illuminate. The diminution of illumination is generally proportional with an inverse of the square of the distance between the illuminating source and the illuminated interface.
According to an embodiment of the present invention, a more efficient single light source with a improved conversion of electrical power to optical power replaces the use of multiple LEDs to achieve a higher energy conversion and corresponding lower power consumption. By using a collimated light beam and using total internal reflection to guide the beam and branches of the beam to viewing surfaces, the total electrical-optical power efficiency of the embodiment is dramatically higher than current solutions. A manufacturer has fewer components to purchase, maintain quality on, and assemble. Also weight, size, volume, number or required electrical connections, etc. may be reduced. The outcome is that inventories are smaller, and manufacturing defects are diminished also increasing reliability. Also, fewer conductive traces are needed to carry electricity to remote parts of the user-interface, resulting in fewer opportunities for defects and failures during manufacturing or use caused by open circuits or short circuits.
An object and advantage of the invention is that the optical power emitted by a light source is propagated through a medium and reflected to illuminate a generally flat area to provide high visibility of silhouetted button markings and LCDs, among others. An attendant advantage is that the generally flat area may have an irregular perimeter.
Another object and advantage of the invention is a light source may be located at greater distances from its target without appreciable light leaking to unintended areas.
Another object and advantage of the invention is that a single light source may be directed to multiple targets without losses typically associated with reflection.
Still another object and advantage of the invention is that light may be provided through a structure that is thin as compared to either its height or length.
In another embodiment of the invention light is guided to a main output surface, and also to a secondary surface not coplanar with the main output surface.